Electrostatic precipitators are efficient and economical in removing particulates from the effluent of combustion processes, such as boilers, furnaces and the like. Electrostatic precipitators were first developed and implemented nearly 100 years ago by the predecessor-in-interest of the assignee of this Application, Hamon Research-Cottrell, Inc.
An electrostatic precipitator typically includes a chamber having a plurality of vertical spaced parallel large conductive panels or collecting electrodes which are rigidly mounted in vertical spaced relation in the chamber. At the centerpoints running between the conductive panels or collecting electrodes are a series of individual discharge electrodes that generally run vertically the full height of the collecting electrodes. For many years, the basic discharge electrode system for electrostatic precipitators consisted of flexible weighted wires hung vertically downwardly from an upper high voltage structure of the precipitator, which wire-discharge electrodes are provided with tensioning blades at the lower ends. More recently, as disclosed in U.S. Pat. No. 4,375,364, assigned to the predecessor-in-interest of the Assignee of this Application, such flexible wire-type discharge electrodes were replaced with rigid “mast-type” discharge electrodes supported on an insulating assembly keeping them electrically isolated from the collecting electrodes. A high voltage direct current is applied to the opposing surfaces of the collecting and discharge electrodes, such that a positive charge is applied to the collecting electrodes and a negative charge is applied to the discharge electrodes. In a typical application, the mast-type discharge electrodes are generally cylindrical, having a plurality of thin spaced pointed radial spikes which create an electrical field between the negatively charged discharge electrodes and the spaced panel-shaped collecting electrodes. However, flexible wire-discharge electrodes are still in use. When particulate-laden waste gases are received at low velocity through this electrical field, the particulates in the waste gas stream become negatively charged and are thus attracted to the positive charge on the surfaces of the positively charged collecting electrodes. When the migration of the negatively charged particulates is complete, the inherent resistivity of the particulates will prevent complete loss of the negative charge to the collecting electrode surface. The retained opposing negative charge in the particles will cause the particulates to agglomerate on the surface of the collecting electrodes.
As will be understood by those skilled in this art, in recent decades the environmental laws have become even more stringent in limiting the discharge of particulates into the atmosphere, such that even slight emissions of particulates into the atmosphere can result in large fines and production cutbacks or shutdowns. These more stringent regulations have resulted in major changes in the physical design of electrostatic precipitators, resulting in “sectionalization”, which are large electrostatic precipitators with many small electrical sections to increase efficiency and reduce the loss percentage in the event of failure of one section of the electrostatic precipitator. Although the flexible wire-type discharge electrodes are more efficient, the rigid mast-type discharge electrodes are more reliable, resulting in a preference for rigid mast-type discharge electrodes. Since the construction of the rigid mast-type discharge electrode is larger than the wire-type discharge electrodes, the rigid mast-type discharge electrodes are less efficient at producing an electrical corona at the same voltage, and thus, it became necessary to change the geometry of the electrostatic precipitator to larger conductive plate collecting electrodes, increase the spacing between the collecting electrodes, and raising the voltage to a higher level to achieve satisfactory corona discharge from the rigid mast-type discharge electrodes in the wider spaced precipitators.
As will be understood, however, even more reliable rigid mast-type discharge electrodes eventually require replacement due to general aging or failure due to temperature surges caused by process upset conditions or precipitator fires. However, placement or replacement of rigid mast-type discharge electrodes is difficult and expensive, requiring lengthy down-time for the electrostatic precipitator and the entire unit and process generally has to be shut down. Replacement of rigid mast-type discharge electrodes also generally requires large holes or openings to be cut in the roof of the electrostatic precipitator, often holes must be cut in the surrounding building structure and cranes are required to lift and lower the large rigid mast-type discharge electrodes, which may be 12 to 54 feet in length and are generally about two inches in diameter having radial discharge emission elements or pointed spikes, as described above.
There is, therefore, a long-standing need for replacement discharge electrodes which reduce down-time of the electrostatic precipitator, labor and cost. The rigid mast-type replacement discharge electrodes of this invention may be manufactured at a remote facility, the components easily shipped to the electrostatic precipitator, easily inserted in small or existing openings within the electrostatic precipitator casing and reassembled internally with minimum and significantly reduced labor, tools and electrostatic precipitator down-time.